The present invention relates to a tire with radial carcass reinforcement, and more particularly to a xe2x80x9cheavy-vehiclexe2x80x9d tire, intended to be fitted on vehicles such as lorries, road tractors, buses, trailers and others, and in which a novel reinforcement structure for the beads is adapted in order to improve the life of said beads.
Generally, a tire of the type in question comprises a carcass reinforcement formed of at least one ply of metal cables which is anchored in each bead to at least one bead wire, forming an upturn. The carcass reinforcement is radially surmounted by a crown reinforcement, composed of at least two plies of metal cables which are crossed from one ply to the next, forming angles of between 10xc2x0 and 45xc2x0 with the circumferential direction. The carcass reinforcement upturns are generally reinforced by at least one ply of metal cables oriented at a small angle relative to the circumferential direction.
In the case of the presence of a single bead reinforcement ply, the latter may be located along the carcass reinforcement upturn with a radially upper end located above or below the radially upper end of the carcass reinforcement upturn. As for the radially lower end of such a ply, it is generally located either on a straight line parallel to the axis of rotation and passing approximately through the center of gravity of the meridian section of the anchoring bead wire of the carcass reinforcement, in the case of a tire having beads intended to be mounted on rim seats inclined at 15xc2x0xc2x12xc2x0, or on a straight line parallel to the axis of rotation and passing through a point located between the center of gravity of the meridian section of the anchoring bead wire and the point of maximum axial width of the carcass reinforcement, in the case of a tire having beads intended to be mounted on rim seats inclined at 0xc2x0 or at 5xc2x0xc2x11xc2x0. In this second case, the reinforcement ply of the bead is then wound around the bead wire, so as to have an axially outer strand and an axially inner strand, the radially upper end of the axially inner strand being generally located beneath the radially upper end of the axially outer strand.
The known solution aims to avoid deradialization of the cables of the carcass reinforcement upturn and to minimize the radial and circumferential deformations to which the end of said upturn and the outer rubber layer covering the bead and providing the connection to the rim are subjected.
In other cases, the metallic reinforcement ply has been replaced by a plurality of plies, textile ones, for example, located axially either on the same side of the upturn or on either side of said upturn, or alternatively partially along the upturn and partially along the carcass reinforcement. Another variant consists in placing two reinforcing plies along the upturn, on either side of said upturn, and a third ply along the carcass reinforcement axially to the outside of said reinforcement.
The life of xe2x80x9cheavy-vehiclexe2x80x9d tires, owing to the progress achieved, and to the fact that certain types of travel are made less of a handicap as far as wear of the tread is concerned, has become such that it is also necessary to improve the life of the beads, and more particularly of tires subject to prolonged travel, this travel frequently inducing a high temperature of the beads owing to the temperatures reached by the mounting rims.
In order to improve the life of a tire required to bear heavy loads and having beads intended to be mounted on flat rim seats or rim seats inclined at 5xc2x0, FR 2 356 528 proposes arranging on the inside of the carcass reinforcement and its upturn a reinforcement armature of radial metal elements having a great elongation, said armature being wound around the bead wire to form two strands, the axially outer strand having one end radially above, on one hand, the upturn of the carcass reinforcement and, on the other hand, the upper end of a second reinforcement armature of elements which are oriented at a certain angle relative to the circumferential direction.
To the same end, French Application FR 2 776 238 proposes, contrary to the above teaching, a tire comprising at least one radial carcass reinforcement, formed of at least one ply of inextensible reinforcement elements and anchored in each bead to a bead wire to form an upturn, the end of which is located at a radial distance Hi~c from the base of the bead, each bead being reinforced by at least two additional reinforcement armatures, at least one first armature formed of radial metallic reinforcement elements and at least one second armature formed of elements forming an angle xcex1 with the circumferential direction such that 0xc2x0xe2x89xa6xcex1xe2x89xa645xc2x0, characterized in that, viewed in meridian section, the first reinforcement armature formed of radial metallic elements is wound around the anchoring bead wire of the carcass reinforcement on the outside of said carcass reinforcement to form two strands, such that the radially upper end of the axially outer strand is radially located at a distance HLE from the base of the bead of between 65% and 95% of the distance HRNC, the second armature not being wound around said anchoring bead wire.
The carcass reinforcement of the radial tire as described above, mounted on its operating rim and inflated to the recommended pressure, has in one sidewall a regularly convex meridian profile between approximately the zones of connection with the meridian profile of the crown reinforcement and with the bead. In particular, starting from the radius where the carcass reinforcement is subject to the influence of the bead reinforcement ply (plies) having reinforcement elements which are inclined relative to the radial direction, said reinforcement has in the bead a concave meridian profile, substantially curved in the opposite direction to the curvature in the sidewalls, that is to say, substantially parallel to the curvature of the rim flanges from a point of inflection located radially approximately at the level of the radially upper end of the bead reinforcement ply having inclined elements, which is placed axially to the outside along the carcass reinforcement upturn. Generally, the meridian profile of any bead reinforcement armature, located axially to the inside or to the outside of the non-upturned part of the carcass reinforcement, is substantially parallel to the meridian profile of said non-upturned part.
Studies and tests have resulted in improvements in the life of said tire, having beads intended to be mounted on flat rim seats or rim seats inclined at 5xc2x0, by using differently the bead reinforcement armature having radial elements. The tire of height H on rim, according to the invention, and comprising at least one radial carcass reinforcement, formed of at least one ply of inextensible reinforcement elements and anchored in each bead B to a bead wire to form an upturn, the end of which is located at a radial distance HRNC from the base D of the bead wire, each bead B being reinforced by at least two additional reinforcement armatures, at least one first armature formed of radial metallic reinforcement elements and at least one second armature formed of metallic elements which form with the circumferential direction an angle xcex1 such that 0xc2x0xe2x89xa6xcex1xe2x89xa645xc2x0, is characterized in that, viewed in meridian section, the first reinforcement armature is formed of at least one ply of inextensible elements which is wound around the anchoring bead wire of the carcass reinforcement on the inside of said carcass reinforcement to form two strands, such that the axially inner strand, between the radially lower end A of its radially upper edge adjacent to the carcass reinforcement and its point of tangency T to the anchoring bead wire, follows a rectilinear trace AT referred to as xe2x80x9cshortest-pathxe2x80x9d, and that the radially upper end of said axially inner strand is radially located at a distance HLI from the base of the bead wire D of between 0.216 and 0.432 times the height H, the axially outer strand which is located axially to the inside of the upturn of the carcass reinforcement having its radially upper end radially closer to the axis of rotation than the end of the carcass reinforcement upturn and the distance HLE between said end of the base D of the bead wire being between 0.2 and 0.8 times the height HRNC of the upturn of the carcass reinforcement, the second armature of elements inclined relative to the radial direction not being wound around said anchoring bead wire and arranged axially to the outside of the upturn of the carcass reinforcement.
xe2x80x9cRectilinear tracexe2x80x9d is to be understood to mean a trace which may differ slightly from a straight line, and in the case of tires to which the invention relates the trace of the axially inner strand of the ply of radial reinforcement elements of the bead will also be said to be rectilinear if it is curved, concave or convex, having a deflection relative to the straight line of at most 2 mm.
The radial reinforcement elements of the first ply of the bead reinforcement armature are preferably inextensible metallic elements, made of steel and in the form of cables.
It is advantageous, in order to improve the resistance of the carcass reinforcement to rupture of reinforcement elements occurring in its portions which form an integral part of the beads, to impart to said portions the same profile as that of the bead reinforcement plies having radial elements, that is to say, a rectilinear profile.
In order to promote the taking-up of the meridian stresses of the carcass reinforcement upturn, and thus to improve the resistance to the initiation and propagation of cracks in rubber which start at the end of the carcass reinforcement upturn, it is particularly advantageous to add to the first reinforcement ply of radial elements a second ply of said elements. In this case, the first ply of elements, the two strands of which are axially located between the carcass ply and its upturn, will have the radially upper end of the axially outer strand very close to the anchoring bead wire and the distance between said end and the base of the bead will be less than the height of the rim flange on which the tire will be mounted. As for the second ply, it will be wound around the anchoring bead wire on the outside of the carcass ply and its upturn, so as to form two strands, the end of the axially outer strand being distant from the base of the bead by a distance HLE2 of between 0.4 and 1.2 times the distance HRNC, and the end of the axially inner strand HLI2 being distant from said bead wire base by a quantity less than the height of the rim flange. Since said second reinforcement ply is located axially to the outside of the concave carcass upturn, it will also preferably have a shortest-path trace, but without necessarily being rectilinear. As in the case of the first ply, the reinforcement elements of the second ply are inextensible metallic elements, and preferably steel cables, the best results being obtained by using steel cables in all the plies present in the bead.
The details of the invention will be better understood with reference to the following description, which refers to the drawings, which illustrate examples of embodiments in non-limitative manner.